Assembly for electrically connecting a test component to a testing machine for testing electrical circuits on the test component

ABSTRACT

In one embodiment, the invention provides a test assembly for electrically connecting a test component to a testing machine for testing electrical circuits on the test component. The assembly comprises a contactor assembly to interconnect with the test component, a probe assembly to mechanically support the contactor assembly and electrically connect the contactor assembly to the testing machine, and a clamping mechanism comprising a first clamping member and a second clamping member, the clamping members being urged together to exert a clamping force to deform contactor bumps of an electrical connection between the probe assembly and the contactor assembly.

FIELD OF THE INVENTION

[0001] This invention relates to test equipment. In particular, itrelates to test equipment for testing electrical circuits includingintegrated circuits.

BACKGROUND

[0002] When fabrication of electronic devices, such as computerprocessors and memories, have been completed, the electronic devices aresubjected to burn-in and electrical testing in order to identify andeliminate defective devices before shipment. The term “burn-in” relatesto operation of an integrated circuit at a predetermined temperature ortemperature profile, typically an elevated temperature in an oven.Certain operating electrical bias levels and/or signals are supplied tothe electronic devices while they are at the elevated temperature. Theuse of the elevated temperature accelerates stress to which the devicesare subjected during burn-in, so that marginal devices that wouldotherwise fail shortly after being placed in service fail duringburn-in, and are therefore not shipped.

[0003] Test equipment for burn-in testing of electrical circuitsgenerally comprise a connection arrangement for electrically connectingan electrical circuit to be tested such as an integrated circuit on awafer or test substrate, to a test probe circuit.

SUMMARY

[0004] In one embodiment, the invention provides a test assembly forelectrically connecting a test component to a testing machine fortesting electrical circuits on the test component. The assemblycomprises a contactor assembly to interconnect with the test component,a probe assembly to mechanically support the contactor assembly andelectrically connect the contactor assembly to the testing machine, anda clamping mechanism comprising a first clamping member and a secondclamping member, the clamping members being urged together to exert aclamping force to deform conductive bumps of an electrical connectionbetween the probe assembly and the contactor assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005] The invention is described by way of example with reference tothe accompanying drawings wherein:

[0006]FIG. 1 is a block diagram of an interposer, an electricalcontactor and a wafer comprising circuits to be tested;

[0007]FIG. 2 is a block diagram of a contactor assembly in accordancewith one embodiment of the invention;

[0008]FIG. 3 is a block diagram illustrating a stage in the formation ofthe contactor assembly of FIG. 2;

[0009]FIG. 4 is a perspective view of a vacuum plate connected to aring, in accordance with one embodiment of the invention;

[0010]FIG. 5 is a top plan view of the vacuum plate and ring of FIG. 4;

[0011]FIG. 6 is a section on 6-6 in FIG. 5;

[0012]FIG. 7 is a block diagram illustrating how a ring and interposerseated therein may be aligned with a contactor, in accordance with oneembodiment of the invention;

[0013]FIG. 8 is a perspective view of an alignment machine in accordancewith one embodiment of the invention;

[0014]FIG. 9 is an end view of the alignment machine shown in FIG. 8 ofthe drawings with a microscope mounted thereon;

[0015]FIG. 10 is a perspective view of the alignment machine of FIG. 8mounted on a probe plate;

[0016]FIG. 11 is an end view of FIG. 10;

[0017]FIG. 12A is a block diagram of the probe plate showing a flexibleconnector in accordance with another embodiment of the inventionelectrically connecting a contactor assembly to the probe plate;

[0018]FIG. 12B is a block diagram of a probe plate showing a flexibleconnector in accordance with one embodiment of the inventionelectrically connecting a contactor assembly to the probe plate;

[0019]FIG. 13B is a block diagram of an end of the flexible connector ofFIG. 12A;

[0020]FIG. 14 shows an arrangement of electrical contact elements on anelectrical contactor in accordance with one embodiment of the invention;

[0021]FIGS. 15 and 16 are block diagrams showing different stages in theformation of an electrical connection between the flexible electricalconnector and the electrical contactor of FIG. 12;

[0022]FIG. 17 is a block diagram of the probe plate of FIG. 12 whereinwithout the electrical connector and showing fiducial markings on thecontactor assembly; and

[0023]FIG. 18 is a block diagram of a test probe assembly in accordancewith one embodiment of the invention.

DETAILED DESCRIPTION

[0024]FIG. 1 of the accompanying drawings illustrates an interposer 10and an electrical contactor 26 which together form a contactor assembly,according to an embodiment of the invention, used to test electricalcircuits, for example, on a wafer 32.

[0025] As will be seen from FIG. 1, the interposer 10 includes asubstrate having a first side 12 and a second side 14. The interposer 10includes a number of electrical terminals 16 on the first side 12. Theinterposer 10 also includes resilient interconnection elements in theform of interconnection spring elements 18. Each interconnection springelement 18 extends from an electrical terminal 16 on the side 12 andterminates in a free end. The purpose of each interconnection springelements 16 is to make good electrical contact with correspondingelectrical terminals on the electrical contactor 26. In otherembodiments, the resilient interconnection elements include pogo pinsand compliant conductive bumps.

[0026] The interposer 10 also has an interconnection spring element 20on each electrical terminal 16 on side 14. The interconnection springelements 20 are similar to the interconnection spring elements 18 exceptthat the interconnection spring elements 20 are for making electricalcontact with corresponding electrical terminals on the wafer 32.

[0027] The interposer also includes mechanical alignment stops 22 on thesides 12 and 14 to prevent overtravel of the interconnection springelements 18 and to prevent the interposer from touching certain areas ofthe wafer 32.

[0028] The electrical contactor 26 includes a contactor substrate whichincludes a side 28. Electrical contactor 26 also includes electricalterminals 30 on the side 28.

[0029] The wafer 32 is shown to include a side 34 which has theelectrical circuits to be tested. The wafer 32 has electrical terminals36 on the side 34 whereby electrical connection to the electricalcircuits may be made.

[0030]FIG. 2 of the drawings shows a contactor assembly 40 in accordancewith one embodiment of the invention. The assembly 40 includes aninterposer 10 and a retaining component in the form of a ring 42. Theinterposer 10 is secured or held in a predetermined or aligned positionrelative to the electrical contactor 26 by a ring 42. It will be seenthat in the predetermined or aligned position, each interconnectionspring element 18 has been deformed against a spring force thereof tomake electrical contact with a corresponding electrical terminal 30 ofelectrical contactor 26. The predetermined position is reached by movingthe ring 42 and the interposer 10 seated therein until the alignmentstops 22 bear against the side 28 of the electrical contactor 26. Inother embodiments, the predetermined position is reached when sufficientpressure is exerted by the interconnection spring elements 18 (or thepogo pins or compliant conductive bumps in other embodiments) to keepthe contactor 26 in place. The stops 22 are thus optional. A spacingbetween the interposer 10 and the electrical contactor 26 is such thateach of the interconnection spring elements 18 is under compression.

[0031] The ring 42 is formed with a recessed surface 44 which defines aseat for the interposer 10. The ring 42 has a flat flange-like face 46which bears against side 28 of electrical contactor 26. The ring 42 issecured to the electrical contactor 26 by means of fasteners 43, forexample screws, extending through screw holes 48 (see FIG. 4). The holes48 are dimensioned to accommodate the fasteners 43 with some degree ofplay to permit alignment of fiducial markings on the interposer 10 andcontactor 26, respectively.

[0032]FIG. 3 of the drawings shows a first stage in the formation of thecontactor assembly 40. Referring to FIG. 3, a vacuum plate 50 isreleasably secured to a side of the ring 42 opposing face 46 to form asub-assembly 51. The vacuum plate 50 can be connected to a pump (notshown) by means of a coupling 54 and a hose 52 connected to the coupling54. In use, the pump creates a vacuum in a region 56 between the vacuumplate 50 the interposer 10. The vacuum retains interposer 10 against therecessed surface 44. As can be seen from FIGS. 4 and 5, the vacuum plate50 is shaped and dimensioned to provide access to the fasteners 43.

[0033] As can be seen from FIG. 6 which shows a sectional view throughsub-assembly 51 taken at 6-6 in FIG. 5, the interposer 10 seats snuglyin the ring 42.

[0034]FIG. 7 of the drawings shows a block diagram of how alignment ofthe interposer 10 with the electrical contactor 26 is achieved. Theinterposer 10 is seated in the ring 42 and moved in an x, y, or ⊖direction such that a fiducial marking 58 on the side 12 of theinterposer 10 is aligned with a fiducial marking 60 on the side 28 ofthe electrical contactor 26. Once the fiducial marking 58 is alignedwith the fiducial marking 60, the ring 42 together with the interposer10 is displaced in a z direction so that the ring 42 makes contact withthe electrical contactor 26. A screw 43 located in hole 48 is thenscrew-threaded into a complementary threaded socket 68 formed inelectrical contactor 26. The fiducial markings 58, 60 allow foralignment for the electrical terminals 30 on the electrical contactor 26with the ends of the interconnection spring elements 18 without havingto take an image of the interconnection spring elements 18. Tolerancesin the position of each interconnection spring element in the x-y planeor the angle at which it projects from the x-y plane do not effect thealignment process. The mechanical stops 22 on the side 18 of theinterposer 10 may be used to limit movement of the interposer 10 towardsthe electrical contactor 26 when forming the assembly 40, such that eachof the interconnection spring elements 18 is under the desiredcompression.

[0035]FIG. 8 of the drawings shows a perspective view of an alignmentmachine 70, in accordance with one embodiment of the invention, whichmay be used to align the ring 42 and interposer 10 combination with theelectrical contactor 26. The alignment machine 70 includes a base 72which is shaped and dimensioned to rest on a probe plate 152 which, inuse, houses the electrical contactor 26. The alignment machine 70 alsoincludes a raised platform or plate 74 which is secured to the base 72by means of mounting brackets 76. The platform 74 supports a carriage78. The carriage 78 is seen in FIG. 9 of the drawings which shows a sideview of the alignment machine 70. The carriage 78 is secured to anunderside of the platform 74 by means of a mounting arrangementcomprising angle brackets 88 and horizontal springs 90. The anglebrackets 88 are secured to the platform 74 and provide an anchor for oneend of the springs 90, the other end of the springs 90 being secured toa floating plate 80 of carriage 78 as can be seen in FIG. 9 of thedrawings.

[0036] The carriage 78 further includes ring holders 82 which aresecured to the floating plate 80 of vertical members 84 extendingbetween the ring holders mounting plate 82 and the floating plate 80.

[0037] Roller bearings 94 disposed between the platform 74 and thefloating plate 80 allow for slidable displacement of the floating plate80 relative to the platform 74. Vertical springs 95 urge the floatingplate 80 into contact with roller bearings 94. It will be appreciatedthat the spring mounting arrangement of the floating plate 80 to theplatform 74 allows for movement of the floating plate 80 in an x-yplane. Such movement in the x y plane is controlled by means of anadjustment mechanism which, in one embodiment, includes micrometers 96,98, and 100, each of which can be operated to urge a tip thereof to bearagainst an edge of the floating plate 80 thereby to cause thedisplacement of floating plate 80. For example, as can be seen in FIG. 9of the drawings, a tip 98.1 of the micrometer 98 may be displaced in a ydirection to bear against an edge of the floating plate 80 thereby tocause the floating plate 80 to be displaced in the y direction. Becausethe ring holders 82 are rigidly connected to the floating plate 80,displacement of the floating plate 80 also causes correspondingdisplacement of the ring holders 82.

[0038] In use, the interposer 10 which is seated in the ring 42 by meansof a suction force created with the aid of the vacuum plate 50 and apump (not shown) is connected mechanically to the ring holders 82 of thecarriage 78. Thereafter, the alignment machine 70 is positioned on aprobe plate 152 as is shown in FIG. 10. In this position, the ring 42and the interposer 10 which is seated in the ring 42 is positioneddirectly over the electrical connector 26 which is seated in the probeplate 152.

[0039] A magnification system comprising a microscope 102 which includesa scope section 104 and a base 106 is secured on the platform 74 as canbe seen in FIG. 9 of the drawings.

[0040] The microscope 102 magnifies the fiducial markings 58, 60 on theinterposer 10 and the electrical connector 26, respectively. Themicrometers 96, 98 and 100 may then be operated to move the carriage 78,which carries the ring 42 and the interposer 10 with it, so that theinterposer 10 may be positioned over the electrical connector 26 in apredetermined or aligned position in which the fiducial markings, 58, 60on the interposer 10 and the electrical contactor 26, respectively, arein alignment.

[0041] The alignment machine 70, further includes micrometer heads 108which may be operated to move the carriage 78 in a z direction whichcauses the interposer and ring combination to be displaced in the zdirection towards the electrical contactor 26. In use, displacement inthe z direction is continued until alignment the stops 22 contact theside 28 of electrical contactor 26, or the desired z position isreached. When this position is reached, the screws 43 are screwed intothe sockets 68 in the electrical contactor 26, thereby to secure thering 42 and the interposer 10 seated therein to the electrical contactor26.

[0042] Once the ring 42 and the interposer 10 are secured to theelectrical contactor 26, the vacuum plate 50 and the alignment machine70 are removed. The probe plate 152 includes an external interfacecomponent 164 comprising a plurality of electrical connectors in theform of electrical pins 166 as can be seen in FIG. 12. A flexibleconnector 110 electrically connects the contactor assembly 40 to theinterface component 164 which in turn is electrically connected to aburn-in chamber of a testing machine (not shown) via the pins 166.

[0043] The flexible connector 110 includes a flexible substrate 112having sides 112.1 and 112.2 as can be seen in FIG. 13A. Further, theflexible substrate 112 has a first end 115 and a second end 116.Flexible line conductors 114.1 and 114.2 are formed on the sides 112.1and 112.2 respectively, as can be seen in FIGS. 13A and 13B of thedrawings. Each flexible line conductor 114.1 has a first end which iselectrically connected to the interface component 164 and a second endremote from the first end. Each flexible line conductor 114.1 includes aterminal at its second end comprising two conductive bumps 118.1 as canbe seen in FIG. 13B of the drawings. Each flexible line conductor 114.2,likewise, has a first end which is electrically connected to theinterface component 164 and a second end remote from the first end whichis connected by a via 113 extending though the substrate 112 to aterminal comprising two conductive bumps 118.2 on the side 112.1. Itwill be appreciated that by having flexible line conductors on each side112.1 and 112.2 of the substrate 112 it is possible for the substrate112 to carry more line conductors 114.1 and 114.2.

[0044] The flexible connector 110 is sufficiently flexible so that itcan fold onto itself without damage to the flexible substrate 112, andis typically made of a material such as polyimide. According to someembodiments, the flexible substrate 112 may have a thickness of 25.4microns or 49 microns, although a thickness of up to 125 microns isstill flexible in a sense that folding onto itself will still bepossible without damage to the flexible substrate 112.

[0045] Typically, the bumps 118.1, 118.2 are formed of gold and have awidth of about 100 micrometers and a height of about 60 micrometers.Gold is preferred as a material for the bumps 118 since it does notoxidize and is able to tolerate temperatures of between 150° C. to 350°C. Further, gold maintains its elasticity within a temperature range ofbetween 180° C. to 240° C. The flexible connector 110 includes a layer119 which covers the line conductors 114.1 and 114.2. The layer 119 ismade of a non-conductive flexible material as can be seen in FIG. 15.

[0046] The flexible connector 110 is electrically connected to therigidly, substantially unbendable electrical contactor 26 of thecontactor assembly 40. For this purpose, the electrical contactor 26 hasa plurality of electrical contact elements 120 that are compatible forelectrical connection to the conductive bumps 118.1 and 118.2 of theflexible connector 110. FIG. 15 shows a layout of the electrical contactelements 120 on the electrical contactor 26. Referring to FIG. 15, itwill be seen that the electrical contact elements 120 are generallyrectangular and are arranged in two rows 125. Each of the elements 120has a flat contact surface 120.1. The contact surfaces 120.1 of all theelectrical contactor elements 120 are in the same plane. In oneembodiment, each electrical contact element 120 has lateral dimensionsof 125 and 500 microns and a height of 30 microns. In this embodiment,the electrical contact elements 120 are spaced on a pitch of 100microns. The electrical contactor elements 120 are typically formed ofgold which provides a fairly robust connection with the conductor bumps118.1 and 118.2. The electrical connection between the flexibleconnector 110 and the electrical contactor 26 has a low profile and inone embodiment is only about 6 millimeters high.

[0047]FIG. 15 of the drawings shows a block diagram of a stage in theformation of the electrical connection between the flexible connector110 and the electrical contact elements 120.

[0048] Basically, in order to form the electrical connection between theflexible connector 110 and the electrical contactor 26, the second end116 of the flexible electrical connector 110 is clamped onto theelectrical contactor 26 using a clamp. The clamp comprises a firstclamping member in the form of an elongate bar 122 of a work hardenedmetal and a second clamping member which is defined by the electricalcontactor 26. A coefficient of thermal expansion of the metal bar 122 ismatched to a coefficient of thermal expansion of the electricalcontactor 26. In one embodiment, the coefficient of thermal expansion ofthe metal bar 122 is within 0.5 ppm/° C. of the coefficient of thermalexpansion of the electrical contactor 26.

[0049] The elongate metal bar 122, the flexible connector 110, and theelectrical contactor 26 have axially extending holes to receive afastening bolt 124 therein. A nut 126 mates with threads on the bolt 124and urges the conductive bumps 118.1 and 118.2 into contact with theelectrical contactor elements 120 to a position shown in FIG. 16 of thedrawings. The clamping force exerted by the fastening bolt 124 causesthe conductive bumps 118.1 and 118.2 to bear against the electricalcontactor elements 120 which results in an elastic and plasticdeformation of the conductive bumps 118.1 and 118.2. This ensures goodelectrical contact between the conductive bumps 118.1 and 118.2 and theelectrical contactor elements 120.

[0050] Because the fastening bolt 124, the metal bar 122 and theconductive bumps 118.1 and 118.2 may have different thermalcoefficients, and due to the high temperatures achieved during theburn-in testing, the fastening bolt 124 may lengthen during the burn-intesting. This results in a gap between a head 124.1, of the fasteningbolt 124, and the metal bar 122.

[0051] It will be appreciated that such a gap will release the clampingforce exerted by the fastening bolt 124 on the flexible connector 110.In order to compensate for the tendency for such a gap to be created, anexpander member 128 of resilient material may be interposed orsandwiched between the elongate metal bar 122 and the flexible connector110 as can be seen in FIG. 16. The expander member 128, which iscompressed under the clamping force generated by tightening of thefastening bolt 124 and relaxes or expands if lengthening of thefastening bolt 124 occurs. Thus, the expander member 128 takes up anygap between the head 124.1 and the metal bar 122, thereby to maintainthe clamping force of the fastening bolt 124. The expander member is ofa material that is able to withstand the elevated temperatures within aburn-in chamber. Further, since a height of the conductive bumps 118.1and 118.2 may vary, the expander member 128 deforms the flexiblesubstrate 112, differentially to compensate for variations in the heightof the conductive bumps 118.1 and 118.2.

[0052]FIG. 12A shows another embodiment 110 A of a flexible connector.The flexible connector 110 A is similar to the flexible connector 110,except that each end thereof has conductive bumps similar to the bumps118.1 and 118.2. One end of the flexible connection 110A is clamped tothe electrical contactor 26 as described above and an opposite end ofthe flexible connector 110A is clamped, in a similar fashion, to aconnector 121 which carries electrical signals to and from the externalinterface 164.

[0053] The contactor 26 includes fiducial markings 130 (as can be seenin FIG. 17) to facilitate alignment of the conductive bumps 118 with theelectrical contactor elements 120 prior to clamping. The fiducialmarkings 130 are visible through the flexible connector 110. Theflexible connector 110 has complementary fiducial markings 132 (as canbe seen in FIG. 13B) which can then be aligned with the fiducialmarkings 130 on the contactor 26 to ensure alignment of the conductivebumps 118 with the contactor elements 120.

[0054]FIG. 18 of the drawings illustrates the components of test probeassembly 160 in accordance with one embodiment of the invention. Thetest probe assembly 150 includes a probe plate 152 and a chuck plate 154which together define a space therebetween for receiving a contactorassembly such as the contactor assembly 40 shown in FIG. 2 of thedrawings.

[0055] The chuck plate 154 has a pedestal 156 which provides support forthe wafer 32. The probe plate 152 includes a piston 158 which isdisplaceable in a cylinder 160 by a hydraulic fluid which, in use, isintroduced into the chamber 160 through a hose 162 which is releasablyconnectable to the cylinder 160. The piston 158 is connected to anelectrical contactor 26 of the contactor assembly 40.

[0056] In use, air is introduced intro the chamber 160 through hose 162to urge the piston 158 to move in a z direction, thereby to displace thecontactor assembly 40 towards the chuck plate 154 until the mechanicalalignment stops 22 on the side 14 of the interposer 10 make contact withthe side 34 of the wafer 32. A resiliently deformable member in form ofan O-ring 163 positioned between the ring 42 and the chuck plate 154serves to limit or control how much displacement of the contactorassembly 40 is produced by movement of the piston 158. Thus, movement ofthe piston 158 does not require precise control. Further, the O-ring 163provides a seal between the ring 42 and the chuck plate 154. The O-ring163 allows for variations in which the faces 46 of the ring 42 may notbe on the same z-plane by cushioning the ring 42 as it is displacedtowards the chuck plate 154. In some embodiment, the O-ring 163 may bereplaced by springs which provide a reaction against movement of thepiston 158. Once the mechanical stops 22 of the side 14 of theinterposer 10 contact the side 34 of the wafer 32, the interconnectionspring elements are compressed thereby to achieve good electricalcontact between the interconnection spring elements 20 of the interposer10 and the electrical terminals 36 of the wafer 32. Thereafter, the hose162 is removed. The probe assembly 152 also includes a securingmechanism to releasably secure or fasten the chuck plate 154 to theprobe plate 152. The securing mechanism has not been shown in FIG. 12,but includes any suitably clamping arrangement such as the kinematiccouplings of U.S. Pat. No. 6,340,895 which is hereby incorporated byreference. The test probe assembly 150 is then inserted into a testburn-in chamber wherein the electrical connection pins 166 are receivedin complementary electrical sockets.

[0057] Although the present invention has been described with referenceto specific exemplary embodiments, it will be evident that the variousmodification and changes can be made to these embodiments withoutdeparting from the broader spirit of the invention as set forth in theclaims. Accordingly, the specification and drawings are to be regardedin an illustrative sense rather than in a restrictive sense.

What is claimed is:
 1. An assembly for electrically connecting a testcomponent to a testing machine for testing electrical circuits on thetest component, the assembly comprising: a contactor assembly, includinga plurality of first conductors; a plurality of first terminals eachconnected to a respective one of the first conductors; a plurality ofresilient interconnection elements each connected to a respective one ofthe first conductors and have ends to electrically contact the testcomponent; and a support component to support the contact assembly; anexternal interface component on the support component and comprisingelectrical connectors to make electrical connections with the testingmachine; a flexible substrate; flexible second conductors on theflexible substrate and electrically connected to the external interfacecomponent; a plurality of second terminals on the flexible substrateelectrically connected to the flexible second conductors; a plurality ofconductive bumps disposed between the first and second terminals; and aclamp comprising first and second clamping members to urge the first andsecond terminals towards each and deform the conductive bumps.
 2. Theassembly of claim 1, wherein the first terminals each comprise aterminal body which has a flat contact.
 3. The assembly of claim 2,wherein the first clamping member comprising an elongate bar spanningmore than one conductive bump.
 4. The assembly of claim 3, wherein themetal bar is a work-hardened metal of hardened steel.
 5. The assembly ofclaim 3, wherein the clamp further comprises a fastening bolt to urgethe metal bar towards the contact surfaces of each terminal body.
 6. Theassembly of claim 5, further comprising an expander member in the clampwherein the expander material is of a resilient material and is undercompression and decompresses in a direction parallel to the fasteningbolt to compensate for loss of clamping force caused by lengthening ofthe fastening bolt.
 7. The assembly of claim 1, wherein the conductivebumps are of gold.
 8. The assembly of claim 1, wherein the conductivebumps have a height of 60 micrometers and a width of 100 micrometers. 9.The assembly of claim 8, wherein the expander member comprises siliconrubber.
 10. The assembly of claim 4, wherein the contactor assemblycomprises an interposer, an electrical contactor, and a retainingcomponent to retain the interposer in electrical contact with theelectrical contactor, wherein the plurality of the first conductors andfirst terminals are located on the electrical contactor, the pluralityof interconnection spring elements are located the interposer, andwherein the electrical contactor and the flexible substrate includefiducial markings thereon to facilitate alignment of the first andsecond terminals.
 11. The assembly of claim 10, wherein a coefficient ofthermal expansion of the metal bar is matched to within 0.5 ppm/° C. ofthe coefficient of thermal expansion of the contactor substrate.
 12. Theassembly of claim 10, wherein the electrical contactor and theinterposer have complementary fiducial markings to facilitate alignmentof the resilient interconnection elements with electrical contactelements on the electrical contactor.
 13. The assembly of claim 1,wherein the resilient interconnection elements comprise springs.
 14. Atest assembly for electrically connecting a test component to a testingmachine for testing electrical circuits on the test component, the testassembly comprising: a contactor assembly comprising first electricalconductors, a plurality of first terminals connected to first ends ofthe first electrical conductors, a plurality of second terminalsconnected to second ends of the first electrical conductors, andresilient interconnection elements to electrically interconnect thefirst terminals to the test component; a probe assembly comprising aplate component supporting the contactor assembly, and an interfacecomponent on the plate component comprising a plurality of externalelectrical connectors for electrically connecting to the testingmachine; a flexible substrate having a first end which is connected tothe interface component and a second end opposite the first end,flexible conductors on the flexible substrate, the flexible conductorshaving a first part which is connected to the interface component and aterminal part at the second end of the flexible substrate, the terminalpart comprising a plurality of third terminals which are aligned withthe second terminals; a plurality of electrical contactor bumps betweenthe second and third terminals; and a clamping mechanism comprising afirst clamping member and a second clamping member, the clamping membersbeing urged together to exert a clamping force that moves the second andthird terminals together so that the contactor bumps are deformedtherebetween.
 15. The test assembly of claim 14, wherein the resilientinterconnection elements comprise springs.
 16. The test assembly ofclaim 14, wherein the first clamping member comprises a metal bar andthe second clamping member comprises a contact surface of each thirdterminal, the clamping mechanism further comprising a fastening bolt anda complementary nut to urge the metal bar towards the third terminals.17. The test assembly of claim 15, wherein the clamping mechanismfurther comprises an expander member located between a head of thefastening bolt and the nut, the expander member being of a resilientmaterial which is under compression and which expands along an axis ofthe fastening bolt to compensate for loss of clamping force due toelongation of the fastening bolt.
 18. The test assembly of claim 17,wherein the contactor assembly includes an electrical contactor on whichis located the plurality of first electrical conductors, the pluralityof first terminals and the plurality of second terminals, the electricalcontactor and the flexible substrate having complementary fiducialmarkings to facilitate alignment of the second and third terminals. 19.The test assembly of claim 18, wherein the conductive bumps are bondedto the third terminals.
 20. A unit for interfacing a test component witha testing machine for testing electrical circuits on the test component,the interface unit comprising: a support component to support acontactor assembly to make electrical contact with the test component;an external interface component on the support component comprising aplurality of electrical connectors for electrical connection to thetesting machine; a flexible substrate having a first end which iselectrically connected to the interface component and a second endopposite the first end; flexible conductors on the flexible substrate,the flexible conductors having a first part which is electricallyconnected to the interface component and a terminal part at the secondend of the flexible substrate, the terminal part comprising a pluralityof terminals, and a plurality of conductive bumps, each of which isconnected to a respective one of the terminals, wherein the terminalpart is connectable to the contactor assembly and carries electricalsignals between the contactor assembly and the testing machine.
 21. Theunit of claim 20, wherein two conductive bumps are connected to eachterminal by wire bonding.
 22. The unit of claim 21, wherein theconductive bumps are of gold.
 23. The unit of claim 22, wherein theconductive bumps have a width of 100 micrometers and a height of 60micrometers.
 24. A contactor assembly for electrically connecting anelectrical test component to a testing machine for testing the testcomponent, the contactor assembly comprising: a test structure; aplurality of electrical terminals on the test structure; a plurality ofresilient interconnection elements, each having a first end connected toan electrical terminal and a free end opposite the first end toelectrically contact the test component; a plurality of electricalcontact elements on the test structure distant from the electricalterminals; and an electrical path bridging each electrical terminal withan respective one of the electrical contact elements, wherein eachelectrical contact element has a body which defines a flat surface toprovide support to matching contactor elements when the matchingcontactor elements are deformed under a clamping force.
 25. Thecontactor assembly of claim 14, wherein the resilient interconnectionelements comprise springs.
 26. The contactor assembly of claim 24,wherein the test structure comprises a plurality of apertures formedtherein to cooperate with clamping members to clamp the matchingcontactor elements.
 27. The contactor assembly of claim 26, wherein thetest structure further comprises fiducial markings to facilitatealignment of the electrical contact elements with the matching contactorelements.